In emission spectroscopy, a source of energy, usually heat as in a flame or an electric arc or spark, is passed into the sample, which absorbs such frequencies as are possible; the re-emission of this light by the sample is observed. The process of absorption and re-emission produces a bright line spectrum which can be measured when the light is dispersed by a grating or prism. The wavelengths of the emitted light identify the element and the particular electronic transition occurring within it.

The amount of light emitted is related to the amount of the element present, and if sufficient precautions are taken the amount can be semiquantitatively determined by measuring the amount of this light. This can be done photographically or by more complex electronic procedures.

See: emission spectrum
Compare: absorption spectroscopy